(L-448) Effects of Prehabilitation Exercise on Segmental Defect Bone Healing

Exercise can help maintain healthy musculoskeletal tissue¹ and regulate inflammation². The inflammatory response is a known, critical mediator of fracture healing³, however little is known about how frequent exercise affects the inflammatory response to fracture, and subsequent bone healing. Fractures remain a considerable clinical burden, with each American expected to experience two fractures in their lifetime⁴.

Studies have shown exercise to increase bone volume and cortical thickness⁵, therefore this study sought to elucidate if regular exercise prior to surgery would alter bone morphological properties before injury. Further, whether pre-surgical exercise would modulate inflammation and improve bone healing in a femoral defect model. We hypothesized that 4-weeks of prehabilitative treadmill running before surgery would increase bone volume, bone mineral density and functional properties, as well as decrease systemic inflammation. We further hypothesized animals exercising prior to fracture would show improved overall healing after injury as compared to sedentary controls.

To investigate the effects of frequent exercise on bone healing, 9-week-old female Wistar rats (n=8) were pretrained for two weeks running on a treadmill with a 5° incline. Following the pre-training period, rats prehabed for 2-weeks running 5days/week for 30min/day at 18m/min with a 5° incline. These running conditions placed their exertion level at ~70-75% VO2 max. Sedentary controls (n=8) were brought into the treadmill room each day to control for stress. At days 0 and 28, blood was drawn for systemic immune profiling (data pending) and bone morphology was characterized via Micro-CT scans. Post-prehabilitation, we created a 2mm femoral defect stabilized with internal fixation. All subjects remained sedentary post-surgery. Blood was drawn at days 3 and 7 after surgery, and every two weeks following. Bone properties and healing were assessed via in vivo x-ray and Micro-CT scans every two weeks. Longitudinal bone properties were analyzed using a two-way ANOVA with repeated measures (p< 0.05). All data are displayed as mean ± sem.

Contrary to our hypothesis, the prehab group had a significantly lower bone volume (p=0.0452) than sedentary animals after prebilitation and prior to surgery. Prehab animals also had significantly lower mechanical properties, as indicated by both the proximal and distal polar moment of inertia, than their sedentary counterparts. Changes in the mechanical properties and morphology of bone in response to treadmill running are inconsistent in the literature⁵. However, weight-bearing exercise in general has been shown to increase bone volume, density and cortical thickness⁶. We hypothesize that our results are due to the adolescent age of the rats at the start of exercise as previous literature has found exercise to impact adolescent skeletal development⁷.

Despite this, bone volume in the exercise group 4 weeks post-fracture (1.336 mm³) was 2X that observed in the sedentary group (0.6602 mm³), although the difference was not significant at this early timepoint. Further, early callus formation was only observed in the prehabilitated animals at 4-weeks. Our pending systemic immune profiling may elucidate the mechanisms behind our exercise-induced improved bone healing. This study is ongoing but preliminary results suggest routine exercise prior to fracture may expedite bone healing and reduce non-union rates.

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